Oh man that takes me back. The last time I went down that rabbit hole was ~2015, I tried to implement a "fully encrypted" setup and started with Ubuntu (I know I know). Something something LUKS.
I spent ~2 days tinkering with it and never got it to work, something with the setup flow was totally broken if you also tried to encrypt root (or boot? idk like I said it's been _years_).
I also remember fun problems with grub. I was trying to dual-boot and the windows partition was using hardware-bitlocker (samsung SSD). Some kind of weird interaction was going on between grub, whatever the windows bootloader is called, and my motherboard's EFI I think. Anyways grub ended up fucking bitlocker up and I almost lost all my gaming saves. Had to use some kind of arcane recovery process to get back to being able to even _insert_ the key so the SSD would unlock and windows could continue booting.
Ended up saying screw it after a few days and just going back to windows for my gaming PC, vowing to never try dual-boot again.